This invention relates in general to variable inductors, and in particular to variable inductors suitable for use in regulating the intensity of light emitted by a lamp, especially a fluorescent lamp.
Historically, there has been a need to accurately and efficiently reduce lamp light output or light intensity. When observing an object, the quantity of light is crucial to perceive the desired detail and/or effect. This requirement becomes more acute when a lens system is used in conjunction with the human eye, or other light detector. Cameras, video cameras, CCD detectors, and photo detectors all use lens systems to capture light. The performance of these detectors is affected by any flickering or variation in the intensity of the light. Fluorescent lamps are popular light sources, and use inverter power supplies that drive the lamps at 90 V and 20 khz to produce a steady, predictable illumination. It is desirable to be able to adjust and/or to instantly switch the intensity of the fluorescent lamp between different levels while keeping the illumination steady and predictable.
It is known to vary the intensity of light emitted by a fluorescent lamp by means of a tapped inductor. A switch selectively connects the lamp to one or another of the taps on the tapped inductor, and the intensity of light emitted by the lamp depends on the tap to which the lamp is connected.
Variable inductors are known that include two standard, off-the-shelf cylindrical magnetic core pieces each having a ring-shaped recess into which a respective half of an inductive coil extends, an air gap being located between the two cylindrical magnetic core pieces. These known variable inductors additionally include a third magnetic core piece in the form of a central movable slug of magnetic material, which can be moved axially within a cylindrical bore at the center of the two cylindrical magnetic core pieces, to bridge or open the air gap located between the two cylindrical magnetic core pieces, thereby causing a slight change in inductance.